One of the jobs of any suspension system is to mount a vehicle chassis to one or more axles with as wide a base as possible to enhance the stability of the chassis. At the same time, the suspension must mount to the chassis at one of its reinforced frame members to provide sufficient strength to support what can be very heavy loads. For most heavy duty vehicles, the undercarriage of the chassis generally takes the form of a rail type frame which extends longitudinally along the outboard sides of the chassis with one or more axles extending transversely underneath the frame members. The common practice in the art is for one portion of the suspension to be fixedly secured to the rail frame member, a second portion of the suspension to be fixedly secured to the axle, with one or more spring members and shock absorbers extending between the suspension members and frame. Almost without exception, the spring member is aligned with the rail frame member. Thus, the location of the frame predetermines the width of the base of support provided by the suspension.
The practice in the art of positioning the spring directly beneath the center line of the rail frame members also places constraints on the minimum height of the vehicle and maximum spring movement and hence load capacity. As can be appreciated, sufficient space must be provided between the rail frame member and the axle for mounting of the spring member and the movement of the spring from an unloaded to a fully loaded condition with some travel remaining to absorb shocks encountered during vehicle travel. As the space allowed for total spring movement is increased, the minimum height of the vehicle must be increased for any predetermined wheel and axle combination. While the capacity of the vehicle may be increased by providing increased stiffness or resistance to spring deflection, this results in a stiffer suspension action and hence a rougher ride.
Any suspension which is designed for use with a steering axle has still further factors to contend with, as it must not interfere with wheel movement throughout the turning radius, be somewhat more compact to accommodate the space required for the engine and transmission, and also provide a somewhat greater amount of stabilization because of the increased stresses encountered by a steering axle.
To solve these and other problems in the prior art, applicant has succeeded in developing a suspension system for both drive and trailer axles as well as steering axles which permit mounting of the springs outboard from the longitudinal rail frame members of the chassis. In the embodiment for drive or trailer axles, a bolster beam with an axle seat is clamped to the axle which has two rail members extending in outrigger fashion, one on either side of the axle. Rail type bracket members similarly extend in outrigger fashion from the rail frame of the chassis and are aligned with the bolster beam outrigger members. These brackets may be connected at their outer end to the wheel housing or other portion of the chassis available for mounting. Air springs are thus mounted between the bolster beam and the outrigger bracket members at a point somewhere near the center line of the wheels.
As can be appreciated, this provides a significantly wider base of support for the chassis and a base which coincides with the center line of the point of contact of the vehicle at each side thereof. Additionally, an offset hanger and torque rod assembly provide parallelogram stabilization of the axle which maintains the pitch of the axle constant as it deflects vertically during vehicle travel and which resists twisting of the axle as the brakes are applied. Furthermore, the dimensions and travel distance for the spring may be selected independently of the distance between the axle and frame, as long as the axle is not permitted to contact the frame during operation. As the springs are generally out in the wheelhouse area of the chassis, they can be increased in size through their cross-sectional area. Thus, this suspension provides a much wider base of stabilization both from side to side and fore to aft, and offers increased load carrying capacity with a smoother and safer ride.
In the embodiment applicant has developed for the steering axle, a novel stool type axle seat bolts directly to the axle and has an outrigger member extending beyond the rail frame of the chassis to mount a spring within the wheelhouse area. An outrigger bracket attaches directly to the rail frame of the chassis and extends upwardly above the stool type axle seat and aligned therewith to provide the mounting for the other end of the air spring member. Thus, the air spring mounts wholly outside the vehicle chassis frame and within the wheelhouse area. The stool type axle seat also provides a mounting position for a sway bar, a shock absorber, and brackets between which bushings extend for connecting a pair of torque rods to provide parallelogram stabilization. All of these functions are provided by this single, integrally formed stool type axle seat which has sufficient clearance to accommodate the wheel movement required of a steer axle. Its compact construction provides ease in installation and maintenance in addition to providing connection points for a number of other suspension components. This unique design further provides the wide base offered in applicant's other embodiment with its related advantages of greater capacity, smoother and safer ride, and greater stability. Applicant's wide base design is particularly suited to taller types of heavy duty vehicles, such as double decker buses which can experience uneven, changing loading at greater distances from the axles of the vehicles, resulting in serious stability problems in a vehicle carrying a very fragile cargo.
A fuller understanding of applicant's invention may be gained by referring to the drawings and description of the preferred embodiment which follows.